2-16Although many wavemeters are used in performing various functions, the cavity-type wavemeter isthe type most commonly used. Only this type is discussed in some detail.Cavity WavemeterFigure 2-12 shows a typical CAVITY WAVEMETER. The wavemeter is of the type commonly usedfor the measurement of microwave frequencies. The device uses a resonant cavity. The resonantfrequency of the cavity is varied by means of a plunger, which is mechanically connected to a micrometermechanism. Movement of the plunger into the cavity reduces the cavity size and increases the resonantfrequency. Conversely, an increase in the size of the cavity (made by withdrawing the plunger) lowers theresonant frequency. The microwave energy from the equipment being tested is fed into the wavemeterthrough one of two inputs, A or B. The crystal rectifier then detects (rectifies) the signal. The rectifiedcurrent is indicated on current meter M.Figure 2-12.Typical cavity wavemeter.Electronic Frequency CountersAnother device used to measure frequencies above the audio range is the ELECTRONICFREQUENCY COUNTER. Since this instrument will be covered in detail in a later chapter, only a briefdescription is provided at this time.The electronic frequency counter is a high-speed electronic counter with an accurate, crystal-controlled time base. This combination provides a frequency counter that automatically counts anddisplays the number of events occurring in a precise time interval. The frequency counter itself does notgenerate any signal; it merely counts the recurring pulses fed to it.